Voltage-dependent anion selective channels (VDAC) have been isolated from mitochondria of various species. This protein may be a regulating factor in the permeability of mitochondrial membrane. Insertion of VDAC into planar lipid bilayers induces conductance in an electric field. The protein can be rendered into "open" (conductive) and "closed" (non-conductive) states under various experimental conditions. The object of the present study has been to investigate VDAC from rat liver by circular dichroism in order to gain structural information about the open and closed states. Thus far, prior to insertion into lipid, VDAC appears largely denatured, but with 60-72% of the chain or Alpha-helix and no Beta structure. Studies are being continued to examine heat-treated VDAC, which resembles the closed state, as well as the effects of insertion into lipid on secondary structure of VDAC.